Common Types of Malware You Need to Know

Malware can range from simple annoyances like popup advertising to causing severe damage like stealing passwords and data or infecting other computers on the network. It can also impact websites and their visitors.

Here are some of the most common types of malware you need to know. We’ll cover how they attack and what you can do to protect against them.

Viruses

Viruses are microscopic infectious agents that contain DNA or RNA and must invade living cells to reproduce (replicate). Unlike bacteria and fungi, viruses cannot create energy for themselves through the process of adenosine triphosphate. Instead, they derive their power from their host cell by hijacking the host’s cellular functions to do their bidding. This hijacking process causes the infected cell to reproduce the virus, and the host cell dies. Viruses can also infect you by bites from infected animals or insects or by sexual contact with an infected partner, which leads to herpes, chickenpox, shingles, and genital herpes.

Viruses can be spread through email attachments, drive-by downloads, and malicious websites that use social engineering techniques to infiltrate a system. They are hard to fight because they evade signature-based detection and include spreader modules facilitating infection. They can hide or modify shared files in the kernel, hypervisor, and firmware.

Worms

Worms are invertebrates with flat bodies and heads that have no hard skeletons. They often live in water or moist soil or inside other animals. Some can grow longer than an Olympic swimming pool.

Computer worms can be devastating. The Morris worm, released in 1988, reportedly caused problems for systems connected to the internet precursor. In 2000, the worm spread via email attachments that appeared to be text files and by running scripts in instant messaging chat sessions.

Trojans

Nicknamed after the Trojan horse that the Greeks used to smuggle soldiers into Troy, Trojan malware can hide in seemingly harmless download files and carry out malicious attacks behind your device. The most common examples, which steal passwords from instant messaging applications; hacker Trojans, which open backdoors to hack into the victim’s device and steal sensitive information; and downloader Trojans which can automatically install additional malware onto your device.

The most apparent sign of Trojans is a slowdown in your device’s performance. You might also notice unexplained programs running, unexpected popups, or spam interruptions. Another sign of Trojans is a sudden change to your computer settings.

Adware

Adware may not be as severe as other forms of malware, but it still can create significant problems for your device. It can slow your Internet connection, serve up annoying popup ads and even change your home page. Adware is often bundled with freeware programs or sneaked into sketchy torrenting software and file-sharing hacks.

Some varieties of adware steal your browsing information without your consent, and they use it to target you with unwanted advertisements. They can also be used to install more harmful malware like Trojans and ransomware on your device.

Symptoms of adware infection include multiple popup ads that are hard to close, your browser or apps crashing frequently, and getting redirected to full-page ads. Other warning signs include mysterious files or folders, cryptic emails, and other suspicious activity. Adware is considered a form of PUP (potentially unwanted program). It’s legal for adware developers to distribute it with commercial software and piggyback it onto other freeware applications, but they shouldn’t be allowed to create such annoying problems.

Spyware

Spyware is software that infiltrates a device without a user’s knowledge. Once installed, it tracks internet usage and steals login credentials, passwords, and other sensitive data. This information can then be sent to the attacker or sold on the dark web.

Some spyware, such as keyloggers, captures each user’s keystroke on their infected device and saves that data. Others, like adware, use your browsing behavior to post targeted ads on your screen or device.

Browser hijackers, another type of spyware, alter your web browser settings without your consent or agreement. This can lead to unwanted popups, redirections, and even system alterations. And while it’s most often used on Windows computers and laptops, cybercriminals are also increasingly using spyware to target Apple devices.

Rootkits

Rootkits are software toolboxes allowing attackers to access and infiltrate computer systems without detection. They’re one of the most challenging malware strands to remove and can cause significant problems if they remain undetected for too long.

A firmware rootkit stores itself on hardware components like a computer’s hard drive or basic input/output system (BIOS), the software installed on a small memory chip in its motherboard. A bootkit rootkit replaces the computer’s bootloader with a hacked version, activated before the operating system loads. A kernel rootkit hides in an operating system’s kernel, granting attackers the highest level of privileges. Kernel rootkits can also turn off antivirus software and record keystrokes. A software or application rootkit renames files on your computer and hides them by lowering their performance. They can be bundled with other malicious programs or downloaded through infected PDFs, pirated media, and apps on third-party app stores.